The design of a next generation air interface, popularly indicated as 5G, as currently initiated by the 3rd Generation Partnership Project (3GPP) aims to achieve a single framework addressing a wide variety of usage scenarios, requirements and deployment scenarios as generally described in 3GPP TR38.913.
The 5G air interface is expected to operate using single-beam and multi-beam operation, in scenarios below and above 6 GHz, in licenced and (forward compatible) un-licenced mode. In single-beam operation, a cell would transmit synchronization signals via sector wide beams once in a given periodicity. In single-beam operation supporting coverage enhancement, the synchronization signals should be able to be transmitted in a manner comprising repetition. In multi-beam operation, a cell (which may consists of multiple transmission points) transmits synchronization signals in a beam sweeping manner. Furthermore, in beam sweeping operation, repetition may be relied upon for further coverage enhancements, for example such that synchronization signals transmitted to a certain direction per sweep block are repeated to the same direction in the next sweep block.
As a user equipment (UE) is likely not to be aware of the operation applied at a cell in advance of synchronization to that cell, a need exists for a synchronization procedures that enables a synchronization search performed by the UE to be as agnostic as possible to the operation applied at the cell.